In this study, we investigate the effect of the diffusion barrier and substrate temperature on the length of carbon nanotubes. For synthesizing vertically aligned carbon nanotubes, thermal chemical vapor deposition is used and a substrate with a catalytic layer and a buffer layer is prepared using an e-beam evaporator. The length of the carbon nanotubes synthesized on the catalytic layer/diffusion barrier on the silicon substrate is longer than that without a diffusion barrier because the diffusion barrier prevents generation of silicon carbide from the diffusion of carbon atoms into the silicon substrate. The deposition temperature of the catalyst and alumina are varied from room temperature to 150°C, 200°C, and 250°C. On increasing the substrate temperature on depositing the buffer layer on the silicon substrate, shorter carbon nanotubes are obtained owing to the increased bonding force between the buffer layer and silicon substrate. The reason why different lengths of carbon nanotubes are obtained is that the higher bonding force between the buffer layer and the substrate layer prevents uniformity of catalytic islands for synthesizing carbon nanotubes.

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  Journal of Korean Powder Metallurgy Institute.2019; 26(1): 11.     CrossRef
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Silicon carbide(SiC) layer is particularly important tri-isotropic (TRISO) coating layers because it acts as a miniature pressure vessel and a diffusion barrier to gaseous and metallic fission products in the TRISO coated particle. The high temperature deposition of SiC layer normally performed at 1500-1650°C has a negative effect on the property of IPyC layer by increasing its anisotropy. To investigate the feasibility of lower temperature SiC deposition, the influence of deposition temperature on the property of SiC layer are examined in this study. While the SiC layer coated at 1500°C obtains nearly stoichiometric composition, the composition of the SiC layer coated at 1300-1400°C shows discrepancy from stoichiometric ratio(1:1). 3-7 μm grain size of SiC layer coated at 1500°C is decreased to sub-micrometer (<1 μm) -2 μm grain size when coated at 1400°C, and further decreased to nano grain size when coated at 1300- 1350°C. Moreover, the high density of SiC layer (≥3.19 g/cm³) which is easily obtained at 1500°C coating is difficult to achieve at lower temperature owing to nano size pores. the density is remarkably decreased with decreasing SiC deposition temperature.

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• High-temperature thermo-mechanical behavior of functionally graded materials produced by plasma sprayed coating: Experimental and modeling results
  Kang Hyun Choi, Hyun-Su Kim, Chang Hyun Park, Gon-Ho Kim, Kyoung Ho Baik, Sung Ho Lee, Taehyung Kim, Hyoung Seop Kim
  Metals and Materials International.2016; 22(5): 817.     CrossRef